The purpose of the proposed research is to demonstrate efficacy and safety of the adjunctive use of nifedipine for myocardial preservation during hypothermic ischemic arrest in humans. Ventricular function and regional perfusion are to be assessed preoperatively, intraoperatively, and during the first 72 hours postoperatively. Follow up with similar studies are to be performed at one week and six weeks after operation. Three groups of patients are to receive either the current cardioplegic solution which has been used in more than 800 cases or the same solution containing 0.1-0.2 microgram/ml of nifedipine. The choice of solutions will be randomized. The three groups of patients are those that require: 1) double or triple valve replacement, 2) valve replacement and coronary artery bypass, 3) replacement of a prosthetic mitral valve or a second valve replacement in a new position and coronary artery bypass. The determinants of the degree of myocardial preservation are to be cardiac indices, stroke work, ejection fractions, and regional wall motion and perfusion analyses. The principal determinants of safety are to be mortality, duration and dosage of pressor agents, use of intraaortic balloon assistance and incidence of perioperative infarction. The methods of assessment include radionuclide ventriculography, positron emission transaxial tomography, thallium perfusion studies and MB-CK determinations.